1. Field of the Invention
The present invention relates to a viewfinder and an image pickup apparatus which are capable of allowing a user to easily perform focus control.
2. Description of the Related Art
Video cameras for broadcast stations and camcorders display a sharply defined image on a viewfinder by boosting high-frequency components of a captured image so as to allow a user to easily perform focus control. In this case, high-frequency components are extracted from a luminance signal included in a video signal obtained by a video camera and are then amplified so as to generate a peaking signal. The generated peaking signal is added to the video signal. Consequently, a sharply defined image obtained by boosting high-frequency components is generated and is then displayed on a viewfinder, thereby allowing a user to easily perform focus control.
FIG. 4 is a block diagram showing a configuration of an exemplary known viewfinder for displaying such a video image obtained by boosting high-frequency components. This known viewfinder includes a camera section and a viewfinder section. The camera section is provided with the following components that are part of an image pickup apparatus with this known viewfinder: an image pickup lens 51; an image pickup device 52; a video amplifier 53; an A/D conversion unit 54; a digital signal processing unit 55; and a D/A conversion unit 56. The viewfinder section is provided with the following components: a video amplifier 57; a band-pass filter or low-pass filter 58; an A/D conversion unit 59; a matrix unit 60; a peaking signal generation unit 61; a multiplication circuit 62; adding circuits 63, 64, and 65; a display device driving unit 66; and a display device 67.
In the camera section included in the known viewfinder, light incident from a subject via the image pickup lens 51 is separated by the image pickup device 52 into three primary color video signals AR, AG, and AB. The three primary color video signals AR, AG, and AB are amplified by the video amplifier 53 and are then supplied to the A/D conversion unit 54. The A/D conversion unit 54 converts the three primary color video signals AR, AG, and AB into digital video signals DR, DG, and DB, respectively, and outputs the converted signals to the digital signal processing unit 55. The digital signal processing unit 55 performs digital signal processing including matrix processing upon the digital video signals DR, DG, and DB so as to generate a luminance signal DY and color difference signals DU and DV, and outputs the generated signals to the D/A conversion unit 56. The D/A conversion unit 56 converts the digital luminance signal DY and the digital color difference signals DU and DV into an analog luminance signal AY and analog color difference signals AU and AV, respectively. The analog luminance signal AY and the analog color difference signals AU and AV, which have been generated in the camera section, are output to the video amplifier 57 included in the viewfinder section. The video amplifier 57 amplifies the luminance signal AY and the color difference signals AU and AV, and supplies the amplified signals to the low-pass filter 58. The low-pass filter 58 limits the bandwidths of the luminance signal AY and the color difference signals AU and AV to a predetermined bandwidth, and outputs the processed signals to the A/D conversion unit 59. The A/D conversion unit 59 converts the processed luminance signal AY and the processed color difference signals AU and AV into a digital luminance signal DY and digital color difference signals DU and DV, respectively.
The luminance signal DY and the color difference signals DU and DV, which have been converted by the A/D conversion unit 59, are supplied to the matrix unit 60. The matrix unit 60, which is a circuit, generates three primary color video signals DR, DG, and DB from the luminance signal DY and the color difference signals DU and DV, and outputs the generated video signals. The luminance signal DY, which has been converted into a digital signal by the A/D conversion unit 59, is also supplied to the peaking signal generation unit 61, and is then used to generate a peaking signal. The peaking signal generated by the peaking signal generation unit 61 is supplied to the multiplication circuit 62. The multiplication circuit 62 controls the level of the peaking signal by multiplying the peaking signal by a peaking level setting signal. The level-controlled peaking signal is added to the digital video signals DR, DG, and DB, which have been output from the matrix unit 60, by the adding circuits 63, 64, and 65, respectively. The primary color video signals DR, DG, and DB to which the peaking signal has been added are supplied to the display device driving unit 66 as video signals RPK, GPK, and BPK, respectively, which are used to display a sharply defined image obtained by adding the peaking signal. The display device driving unit 66 generates a driving signal for the display device 67, and causes the display device 67 to display, using the video signals RPK, GPK, and BPK, a sharply defined image obtained by adding the peaking signal.
Such a technique for allowing a user to easily perform focus control of a captured image using a peaking signal is disclosed in Japanese Unexamined Patent Application Publication No. 9-139952. More specifically, three primary color signals are generated from a video signal. A peaking signal is added to the three primary color signals. Consequently, edge portions included in a captured image are displayed with a predetermined color. A user can easily perform focus control using the edge portions displayed with the predetermined color.